IMS (IP Multimedia Subsystems) which has been developed for IP (Internet Protocol) multimedia services in the third-generation mobile communication network is now core technology for providing new services in All-IP based next-generation communication environments.
The IMS network which is a packet-switching based packet network may make it possible to provide mVoIP (mobile Voice over IP) as a packet based voice call service to users. However, the inventors have noted that, where All-IP environments have been not completely realized yet, new infrastructures are all constructed to provide supplementary services for a packet based voice call service, it may result in overlapping investments with existing similar infrastructures and also cause the burden of time and cost in constructing such infrastructures.
Additionally, where All-IP environments have been not realized yet, a circuit network providing circuit switching and a packet network providing packet switching may coexist with each other. In this case, a user terminal may use a voice call service by accessing either the circuit network or the packet network. Therefore, the inventors have noted that there is a need to control supplementary services for such a terminal across the circuit network and the packet network.